1. Field of the Invention
The present invention, generally, relates to ink jet printers and, more particularly, to the ink jet print head that is used in high speed printers.
While ink jet print heads have been developed in the past that have operated with a measure of success, the reasons for this success have not been understood, and this lack of understanding in this relatively new technical field has contributed to a lack of success in the production of reliably operable print heads. A print head in accordance with this invention, on the other hand, has enjoyed as high as 100% success in the production of operable ink jet print heads.
2. Description of the Prior Art
In order to understand the significance of the contribution that the present invention makes to the production of operable ink jet print heads, a review of the prior art is believed to be helpful.
U.S. Pat. No. 4,245,225 was granted in 1981 to Fillmore, Young and the present inventor and is assigned to the same assignee as the present invention. The ink jet print head described in this prior patent is effective in preventing the propagation of vibrations in a longitudinal direction within the ink cavity, and it is effective in overcoming the other described problems. However, while that structure is effective from an operational viewpoint, it overlooks production considerations that render only about 3 out of every 10 produced operationally effective. This will be described in more detail in connection with the present invention hereinafter.
U.S. Pat. No. 4,245,227 to Krause and assigned to the same assignee as the present invention describes an ink jet print head structure that is operable at a predetermined specific frequency in order to produce ink droplets of a desired size, spacing and rate of movement. This prior patent does not identify production problems or mention any of the solutions that are described in detail hereinafter.
U.S. Pat. No. 4,460,842 was granted in 1984 to Waanders et al. and concerns a specific structural arrangement for the piezoelectric device to obtain a high, constant pre-load force. The description contained in this prior patent actually teaches away from one aspect of the invention and fails to mention any of the other production problems that are solved by the present invention to obtain the high operability rate of the ink jet print heads produced by following the principles of the invention. This will become more readily apparent from the detailed description to follow.
United States pat. No. 4,587,528 was granted more recently, in 1986, to Beaudet and relates to a structure for developing a more uniform breakup of a plurality of ink jet streams into ink drops. In the description of the plurality of piezoelectric elements with "surrounding acoustic isolation material" that is identified as a polyurethane material, there is no mention of the inoperativeness that can result unless the production techniques of the present invention are included. For example, this prior patent teaches the cutting of a plurality of 0.05 inch slots 42 in the transducer 27 to reduce unwanted wave transmission through the transducer, but then, it teaches the "potting" of the transducer 27 with an acoustical isolation material 28. As will be understood from the detailed description hereinafter, this is teaching away from the present invention.
In all ink jet print heads having a plurality of ink jet nozzles connected to an ink reservoir, one measure of successful operation is when the ink droplets produced from the streams of ink passing through each of the nozzles have substantially the same break-off point, are substantially uniform in size, have substantially uniform spacing between the droplets and are free from ink spatter (sometimes called "satellite free"). It is only when the ink jet print heads have these operational characteristics that they will ensure the desired high print quality in a consistent and uniform manner.
In order to manufacture ink jet print heads to obtain this uniformity between the droplets of the several ink streams, it had been considered necessary in the past that such uniformity is obtained by having the perturbations that are applied to each ink stream be substantially uniform and, also, by making the ink nozzles with care to ensure their uniformity. In addition, the ink droplets have been kept satellite free by making these perturbations sufficiently large and uniform.
Even when prior ink jet print heads are manufactured with all of the features and care during production described above, experience has shown that less than half operate with the needed uniformity and consistency. However, by following the production steps and by making the structural changes in accordance with the present invention, the needed improvements in operational characteristics can be realized.